The present invention relates to a tube heat exchanger and a tube plate for supporting the tubes of a tube heat exchanger. Specifically the invention relates to a heat exchanger with vertical tubes of considerable lengths having weights which in combination with high temperature subject the tubes themselves and the tube plate to considerable stresses. This tube plate is particularly suitable for use in tube heat exchangers which produce carbon black.
Carbon black is the term used for the finely divided powder forms of carbon which are produced by incomplete combustion or thermic degradation of natural gas or mineral oil. Depending on the method of production, different types of carbon black arise, namely so called channel black, furnace black and pyrolysis black (also called thermal black). Furnace black is by far the most important form of carbon black and is used to a considerably larger extent than the other two. The present invention relates specifically to this type of carbon black, which in the present application is referred to simply as justxe2x80x9ccarbon blackxe2x80x9d.
FIG. 1A illustrates a conventional plant for the production of carbon black (i.e. of the furnace black type). Incoming combustion air flows through a tube conduit 1 into the upper part of a tube heat exchanger 2, in which it is preheated before supporting the subsequent combustion of oil in the burner 9 and the combustion reactor 3. The thus preheated air is passed into the combustion chamber 10 via a conduit 5. Oil is added to said reactor via a tube conduit 4. The amount of air corresponds to about 50% of the stoichiometric amount of oxygen gas required for a complete combustion of the oil, whereby carbon black is formed. It is also possible to add water into the reactor 3, which has an impact on the quality of the final product. The mixture of the suspended carbon black in the consumed combustion air is led away from the top of the heat exchanger via a conduit 6, through a cooler 7 which is normally water cooled to a filter arrangement 8, conventionally equipped with textile bag filters. In this filter arrangement the carbon black is filtered off from the gas flow, which is then passed out through a non-return valve 16 for further purification in a plant 11, before it is exhausted into the ambient air via a chimney 12.
The construction of the conventional heat exchanger 2 may be more clearly seen in FIG. 1B. The heat exchanger is of the tube type, with a plurality of substantially vertical tubes 13 whose lower ends are supported on a tube plate 5A. The gases from the combustion process rise up the insides of these tubes, whereby they are cooled by the air that enters via the inlet 1 and passes outside the tubes 13 downwards towards the outlet 5, in the space enclosed by the outer jacket wall 14. In order to increase heat transfer, the air coming through the inlet 1 is subjected to a reciprocal movement by an arrangement of a plurality of mainly horizontal baffles 15. These are made of plates which extend across about xc2xe of the diameter of the heat exchanger whereby each plate is provided with a plurality of holes for the receipt of the tubes 13. The temperature at the inlet 1 of the heat exchanger tubes 13 may be about 1000xc2x0 and the air coming through conduit 1 may be heated to about 800xc2x0. These conditions result in utmost severe stresses for the materials in the heat exchanger. The part of the heat exchanger that is submitted to the highest mechanical stress is the lower part of the jacket and the tube plate 5A where the temperature may amount to 900xc2x0. Thus, with an internal pressure of approximately 1 bar at that temperature, a jacket wall diameter of about 2000 mm, tubes numbering between 50 and 150, plus a height of the tower of approximately 13 m, it can be easily understood that the tube plate must be able to withstand exceptionally large stresses, particularly since the tubes 13 rest with their entire weight on the tube plate. Furthermore, even the lower portions of the actual tubes 13 are exposed to heavy loads via their own weight in combination with the high temperatures. The tubes 13 have individual compensator devices placed at the top of each tube, the function of which is to off-load the thermally induced stresses in the tubes, as a result, for example of clogging.
An equivalent problem involving the actual outer jacket wall 14 has been solved as described in commonly-assigned Swedish Patent Application No. 9504344-4, corresponding to U.S. Pat. No. 5,866,083, the contents of which are hereby incorporated by reference. According to the invention, the heat exchanger includes a further jacket wall, which is substantially cylindrical and is placed inwards and mainly concentrically to the outer jacket wall so that at both ends open, mainly cylindrical spaces are formed in the gap between the two jacket walls, whereby the gas which flows in through the inlet passes through this space before coming into contact with the tubes of the heat exchanger. Occasionally the tube plate has failed to stand up to the heavy loads to which it has been exposed leading to very high repair costs.
Attempts have been made to cool the lower tube plate through a double bottom construction as shown in FIG. 2. In this design, a portion of the incoming air which enters through the inlet 1 is lead away in a vertical pipe 17 and flows down into a double-wall tube plate 18, which includes an upper thermally insulated wall 19 and a lower thermally insulated wall 20, so that a chamber (manifold) 21 is formed between the two walls. Air from the vertical pipe 17 flows into the manifold 21 and hence cools the tube plate, after which the air flows out through an exhaust pipe 22 and is returned to the heat exchanger. However this design has not proved to be sufficiently effective since it does not cool the tube plate adequately. Therefore it has been proposed that, in accordance with Swedish Patent Application 9603739-5, the manifold 21 be split up into a number of channels through the use of dividing walls, whereby each channel is provided with an inlet and an exhaust, and a number of heat exchange tubes pass through each channel. This has solved the problem of excessive temperatures in the base plate in a satisfactory manner, but the lower portions of the heat exchanger tubes are still very hot and can, for example, bend or buckle. It should be borne in mind that a 13 m long heat exchanger tube can weigh approximately 100 kg. Since the tube stands with its entire weight on the tube plate, the tube plate and the lower, very hot parts of the tubes are particularly heavily loaded. When a buckle is induced, stress on the tubes increases and the deformation process can accelerate.
A prime objective of the present invention is thus to produce a heat exchanger in which the lower parts of the tubes are protected from large loads.
A second objective of the invention in question is even to protect the lower tube plate from large loads.
These and other objectives have been successfully achieved in a surprisingly simple manner by designing the heat exchanger so as to include a substantially cylindrical, closed vessel which defines a space, and providing a horizontal support wall disposed adjacent an upper portion of the space. A plurality of tubes are affixed to the support wall and hang downwardly therefrom. A tube plate is situated adjacent a lower portion of the space. The tube plate includes upper and lower walls spaced vertically apart to form a chamber therebetween. Metallic bellows are disposed around respective tubes. Each bellows extends between the tube and the tube plate. The bellows are compressible and expandable to accommodate thermal expansion and contraction of the tubes.